The present invention generally relates to a primary cell and more particularly, to a sealing construction of an alkaline galvanic cell such as a silver oxide cell, mercury cell, alkaline manganese cell, nickel-zinc cell or the like.
Generally, as shown in FIG. 1, an alkaline galvanic cell particularly, of a flat type includes a metallic container M serving as a cathode terminal member (referred to a cathode container hereinbelow) in which a cathode active substance A mainly composed of silver oxide or manganese dioxide, a separator S and an electrolyte impregnated material E are successively accommodated, and a sealing plate or sealing container P serving as an anode terminal member (referred to as an anode sealing plate hereinbelow) in which an anode active substance C composed of a mixture of amalgamated zinc powder and alkaline electrolyte subjected to gelation is housed. The anode sealing plate P is fitted into the cathode container M, through an electrically insulating packing I made of synthetic resin such as polyamide resin, polyolefin resin or the like and closely fitted around the peripheral edge of said sealing plate P, with the upper peripheral edge of said cathode container M being crimped inwardly for hermetically sealing the cell.
For the insulating packing I referred to above, there have conventionally been employed nylon, polypropylene, ethylene tetrafluoroethylene copolymer resin, high density polyethylene, etc. However, since a sufficient sealing property can not be obtained by the known insulating packings as described above, various other methods have also been proposed, for example, a method disclosed in U.S. Pat. No. 3,922,178 employing a fatty polyamide amine as a sealing agent, or another method disclosed in U.S. Pat. No. 3,713,896 using a product of the curing reaction between amine and epoxy as a sealing agent, for example, as shown at L in FIG. 1.
As a result of careful investigations carried out by the present inventors into the prior art as described above, however, it has been found that, although useful for improving the sealing effect, fatty polyamide amine is not fully satisfactory from the viewpoint of a leakage prevention or leakage resistance. On the other hand, in the case where the sealing is effected by applying a mixture of epoxy and polyamide onto the sealing plate P for subsequent hardening, there have been inconveniences such that the amount of application is undesirably altered due to the gradual progress of reaction between the epoxy and polyamide before the actual application of the sealing agent onto the sealing plate P, with a favorable leakage prevention property not being available due to deterioration in the close adhesion with respect to the sealing plate P.
Upon further study into the influence of amine valence in fatty polyamide over the leakage prevention property, the present inventors have discovered the fact that the larger the amine valence is, the less is the copper surface contacting the sealing agent, subjected to amalgamation. More specifically, fatty polyamide amine having amine valence (ASTM D2074-62T) in the range larger than 80 to less than 400 is basic, with a large amount of active hydrogen, and if applied to a cell, closely adheres onto the surface of a copper layer located at the innermost portion of the anode sealing plate P which is of a layered clad plate to retard excessive progress of amalgamation for preventing creeping of the alkaline electrolyte.